1. Field of the Invention
The present invention generally relates to a thermally developing image printing apparatus. It particularly relates to an apparatus for thermally developing a light and pressure sensitive thermally developing material composed of a support and an active material applied thereon. The material is photosensitive and is able to be thermally developed to obtain a picture which can be fixed by pressure.
2. Background of the Invention
As an example of an image recording material prepared by utilizing microcapsules containing photosensitive components, there is known a system having a support carrying synthetic macromolecular resin wall capsules each containing a vinyl compound, a photopolymerization initiator, and a colorant precursor. Such a system is disclosed, for example, in Japanese Patent Unexamined Publication No. 179,836/1982. In the image recording method utilizing the system described above, microcapsules are exposed to image carrying light and are hardened in correspondence to the image and whatever microcapsules remain non-hardened are exploded by pressure to thereby obtain a color picture by the colorant precursors released from the exploded microcapsules. This method employing the system is featured in that a high-quality picture can be obtained through a simple dry process. The system, however, has the disadvantage that the photosensitivity is extremely small compared to a silver halide system.
In order to eliminate the foregoing disadvantage, there has been proposed a new highly photosensitive recording material by which a high-quality picture can be obtained through a simple dry process, as disclosed in Japanese Patent Application Nos. 117089/1985 and 121284/1985 filed by the same applicant of this application. This recording material is a photo-pressure sensitive thermally developing material composed of a support carrying thereon at least a photosensitive silver halide, a reducing agent, a compound which can be polymerized (hereinafter, referred to as a polymerizable compound), and a color-picture forming material. At least the polymerizable compound and the color-picture forming material are composed of photosensitive components contained in the same microcapsules.
To record a picture by using this light and pressure sensitive thermally developing material, the material is exposed with imaging light to form a latent image on the material. The material is then developed by heat to polymerize the polymerizable compound to produce a high molecular compound so as to harden the microcapsules in the position where the latent image exists. Next, the material is put on a picture receptor to which the color-picture forming material can be transferred. The material is pressured against the receptor so that at least a part of the microcapsules in the position where the latent image does not exist are exploded so as to transfer to color-picture forming material to the picture receptor to thereby obtain a picture on the picture receptor.
In order to obtain a high-quality picture in the case where a picture is recorded by using such a photo-pressure sensitive thermally developing material as described above, it is necessary to take sufficient time for a thermally developing process and it is desirable to prevent the photo-pressure sensitive thermally developing material from coming in contact with air (oxygen) as much as possible during the heating process. This is because the reducing agent contained in the photo-pressure sensitive thermally developing material is oxidized or the polymerizable compound in the material is inhibited from being polymerized to thereby prevent a high molecular compound form being produced, so that development cannot be performed efficiently and high-quality pictures cannot be obtained.
Further, in an apparatus for thermally developing such a light and pressure sensitive thermally developing material as described above, in some cases, a heating roller is used for heating. The light and pressure sensitive thermally developing material is conveyed while being in contact with this heating roller so as to be thermally developed. In this case, however heating might be performed at a temperature higher than a predetermined value by an abnormality occurring in the heater for one cause or another. In this case, not only can satisfactory development not be performed but the light and pressure sensitive thermally developing material may be overheated to present a risk of a fire.